The present invention relates to reducing toner rub-off in an electrophotographic apparatus and in one of its aspects relates to a method and a system for reducing toner rub-off in copies produced in an electrophotographic apparatus by spraying printers"" anti-offset powder onto the copies after they pass through the fuser section of the apparatus but before they are stacked or otherwise finished.
In a typical electrophotographic apparatus (e.g. copier), a continuous loop of photoconductor film or the like is commonly used to transfer an image from an input section onto a receiving medium (e.g. a sheet of paper or the like). The film is charged and passed through an input section where an image (i.e. analog or digital) is projected onto the charged film. The film then moves through a developing section where toner is applied to the charged image before the image is transferred to the sheet of paper. The paper is subsequently passed through a fuser section where the toner is typically fixed to the paper by passing the paper between two rollers, i.e. a pressure roller and a fuser roller, at least one of which is heated. Heat can be applied to either the inside or outside of the heated roller. One of the rollers typically has a compliant surface which deflects to form a fusing xe2x80x9cnipxe2x80x9d when the two rollers are pressed together.
A known problem in fuser sections of this type is one which is commonly referred to as xe2x80x9coffsetxe2x80x9d. Offset occurs when some of the heat-softened toner particles remain on the fuser roller and are not fixed onto the paper as desired. As well understood in the art, this offset can severely affect the quality of the copies being made by the machine. To alleviate this problem, a release oil, e.g. silicone oil plus additives, is typically applied onto the fuser roller to prevent the toner from sticking thereto. Some of this release oil may also come off onto both the image and the blank areas of a copy as the copy passes through the nip between the rollers.
Also, since the toner used in these types of electrophotographic apparatus is only partially melted, the toner does not soak into the copy substrate as most inks do, even when the substrate is as absorbent as bond paper. Instead the toner forms a localized, raised portion in the image area on the copy substrate. If the desired image finish is very low in gloss, the image surface is also likely to be rough in order to scatter light.
Since the images on the copy substrate are raised and sometimes rough, they can be easily abraded or xe2x80x9crubbed offxe2x80x9d during any one of several finishing processes which may be carried out in the finisher or finishing section of an electrophotographic apparatus after the copy has passed through the fuser section. These finishing processes may include one or more of the following: re-imaging (double-sided copying), folding, stapling, binding, collating, stacking, etc. Residue from this abrasion can cause objectionable marks on adjacent copies or covers which, in turn, can produce copies of unacceptable quality. This abrasion and associated defect is known in the art as xe2x80x9crub-offxe2x80x9d. Since all that is needed to generate rub-off is a donor (toner image), a receptor, differential velocity between the donor and receptor, and load between the donor and receptor, rub-off is common, in varying degrees, in most, if not all, electrophotographic copiers of this type.
Basically speaking, the mechanisms of rub-off are consistent with those found in abrasive and adhesive wear. Accordingly, several of the factors that influence abrasive and/or adhesive wear also influence toner rub-off. Such factors include (a) toughness of the toner; (b) the coefficient of friction of the toner; (c) how well the toner is attached to the substrate and to itself; (d) the coefficient of friction and surface topography of the toner image; (e) the level of load and relative velocity of the wearing surfaces; and (f) the characteristics of the wearing surfaces.
More specifically, (1) tougher toner with a lower coefficient of friction, (2) a toner that fuses better or is fused better, (3) a smoother image finish, and/or (4) a lower coefficient of friction of the finished image will all reduce toner rub-off. Unfortunately, however, there are certain drawbacks associated with each of these factors. For example, a tougher toner is not only more expensive to grind, it is also more difficult to grind and maintain the extremely small particle sizes that are most desirable for such toners.
Further, when the coefficient of friction of the toner is reduced by adding wax, the charging behavior of the toner may become inconsistent leading to copies of differing quality. Still further, toner that fuses better is more likely to fuse in certain subsystems of the copier apparatus (e.g. developer and cleaning stations) where it should not fuse causing obvious problems. Also, using better-fusing toner and/or increasing heat on the fusing roller can cause more toner to stick to the fuser roller and/or increase the tendency of fused copies to stick to each other in the finisher or output trays. Likewise, providing a smoother toner image surface can increase image gloss to an unacceptable level while increasing the use of fuser release oil can cause undesirable effects in the rest of the electrophotographic process, especially when the copy is recycled in a two-sided copying process.
Some of the above mentioned factors are under the control of the apparatus and material manufacturers while others are under the control of the customer/end user. In any event, it should be readily recognized and appreciated by those familiar with this art that any reduction in toner rub-off which can be achieved with a minimum of expense and/or sacrifice to the operation and maintenance of the copier will be highly beneficial to all concerned.
The present invention provides a method and apparatus for reducing toner rub-off from a copy made by an electrophotographic process. Basically printers"" anti-offset powder (e.g. finely-powdered starch) is applied onto the copy after the copy has passed through the fuser section and the image has been fused to the copy. The powder may be sprayed onto either or both sides of the copy.
Typically, a release oil is applied to the fuser roller within the fuser section of a electrophotographic copier to aid in preventing toner from sticking to the fuser roller. As will be understood, some of this release oil will inherently be transferred to the copy as the copy passes over the fuser roller. Where release oil is present on the copy, the printers"" anti-offset powder is sprayed directly over said fuser release oil on said copy and will stick thereto.
To apply the printers"" anti-offset powder in the present invention, an applicator is positioned downstream of the fuser section (e.g. in the finishing section of the electrophotographic apparatus) which receives the copy after the copy has passed through the fuser section and a toner image has been fused onto the copy. As illustrated, the applicator is comprised of a container which is adapted to be positioned within the finishing section of the copier. The container is adapted to store a quantity of the printers"" anti-offset powder. An air supply conduit, which is connected to an air supply at one end and closed at the other, passes through the container. The outer portion of the air supply conduit, having at least one exit therein, is configured so that it will be positioned substantially parallel to a copy as the copy passes from the fuser section and through the finishing section of the electrophotographic copier apparatus.
The air supply conduit has an inlet which is positioned within said container and provides an opening through which powder can be drawn into the air stream which is flowing through the conduit. The air supply also has an outlet positioned within the container and upstream from the inlet to supply air into said container under pressure to aerate and thereby suspend a portion of the powder within said container.
The air passing through the air supply conduit draws the suspended powder into the conduit through the inlet. The air stream then carries the suspended powder through the conduit to the outer portion thereof. The suspended powder then passes through exit(s) spaced along the length of the outer portion of the conduit and is sprayed directly onto the copy as the copy moves past the air supply conduit.